In the deep-sea, gelatinous organisms can take many strange forms. Recently there has
been a wave of interest in images of an animal with a bag-like body, covered by a meshed
pattern, and without noticeable tentacles. This is not a ghost or trash; it is the scyphomedusa
Deepstaria. It was named after the submersible Deepstar, from which it was first observed
intact in 1966. This large and fragile species can't be collected effectively with nets,
but has been seen on 29 dives in last 20 years using the submersibles of the Monterey Bay
Aquarium Research Institute..
Surprisingly, according to traditional taxonomy and to genetic studies by Keith Bayha and
colleagues, one of Deepstaria's close relatives is the one of the most commonly seen medusae:
the moon jelly Aurelia aurita, which is on display in aquariums around the world.
Although its morphology seems odd, Deepstaria's adaptions of extreme size, mesh-like digestive
system, and lack of tentacles are actually typical of several other deep-sea species
in its same family, the Ulmaridae. Stygiomedusa, for example, has a large thick bell and curtain-like
oral arms. Tiburonia, named after the ROV Tiburon by George Matsumoto and colleagues,
has a massive beach-ball-like bell, but stubby finger-shaped oral arms. Stellamedusa ventana,
named after the ROV Ventana, was nicknamed "bumpy" by Kevin Raskoff and others, for the
warty appearance of its surface.
These warts are also present in many of the other Ulmarids, and they give a clue as to
how these medusae can survive without tentacles. In many cases, the bumps are concentrations
of stinging cells, which cover the surface and inside of the jelly. Anything touching
or landing on the bell gets stung. Deepstaria has another adaptation: it can pull the opening
of its bell closed like a kitchen trash bag to trap things inside. {A few other deep sea
jellies use this same trick to catch things without tentacles.
The NET-like mesh running through the bell is another indication of how Deepstaria and
other Ulmarids survive. This pattern is not the nerve net, but it is a network of interconnected
canals, which connect back to the stomach. By achieving a large size, the medusa maximizes
its ability to entrap prey, and using a branched digestive system lets it distribute nutrients
and energy through and across masses of jelly.
One of the most interesting things about Deepstaria is a close association with a marine isopod
-- a relative of the pillbugs you might find in your garden, except that these grow to
7 cm — almost 3 inches — in length.
We call these isopods, in the genus Anuropus, the "pilots" of the medusae -- there almost
always seems to be one crawling around inside the bell, and they haven't been found on other
species of jellies. The isopod was originally found in trawls of the Challenger expedition
in the late 1800s, and its association with Deepstaria was first reported back in 1969.
Like most crustacean parasites of jellyfish, Anuropus probably damages the jelly, but it
can't be too aggressive or it would eat itself out of its hiding place.
It is important to point out that on other videos, the jelly looks like it is pulsing,
undulating, and contorting itself inside out. This is entirely caused by the activity of
the submersible. Subs use several propellers to shoot water, pushing the vehicle around.
As a result, the water around it is usually swirling in all directions. Unless you approach
with extreme care, jellies will start to undulate, twirl. Naturally Deepstaria hangs motionless
and makes slight and subtle undulations of the body.
This is Steve Haddock of the Monterey Bay Aquarium Research Institute. If you see any
unidentifiable blobs, let us know at jellywatch.org
